1. Field of Application
The present invention relates to an information processing system having a plurality of computers which perform mutual data communication, such as a plurality of microcomputers of an ECU (Electronic Control Unit).
In particular, the invention relates to such an information processing system, in which one computer performs calculation processing based on values that are transmitted from another of the computers
2. Description of Related Art
Types of information processing system are known such as an ECU for controlling equipment of a motor vehicle (e.g., as described in Japanese patent publication No. 2003-138980), made up of a plurality of microcomputers which mutually exchange data. With such an ECU for example, one of the microcomputers may perform control of the vehicle engine operation, and control of the degree of throttle opening control, while a second microcomputer may perform judgement of operating conditions of the vehicle based upon detection signals that are supplied to it from sensors, etc.
When a plurality of microcomputers function cooperatively in such an ECU, and a microcomputer performs calculation processing based on values that are transmitted to it from another of the microcomputers, then it may be necessary for the first-mentioned microcomputer to take into account (in performing the calculation processing) the amount of time required to transfer data from one microcomputer to another, with that time amount being referred to in the following as the data communication delay. For example there will be a certain amount of deviation between the time point at which a calculation is performed by the receiving microcomputer and the time point at which a (received) value used in that calculation was acquired by the transmitting microcomputer, resulting in an error in the calculation results.
Proposals have been made to obtain an estimated value of such a data communication delay beforehand, based upon theoretical calculations, and for the receiving microcomputer to use that estimated value to compensate the calculation processing such as to eliminate the effects of the data communication delay.
However it is found in practice that there is a large amount of error in such estimated values that are derived based upon theoretical calculations. Hence when these are used, the calculation processing must be modified to take into account the extent of such error.
For example, a value derived by a first microcomputer may be transmitted from the first microcomputer to be compared with a reference value by a second microcomputer and a judgement made by the second microcomputer, based on the comparison results, as to whether the derived value is normal. If compensation is applied for the data communication delay based upon theoretical calculations performed beforehand, then due to the excessive amount of possible error, it is necessary to make the range of detected values that are judged “abnormal” excessively wide.
Alternatively, it may be attempted to decrease the effects of such an error by increasing the amount of time taken to perform the judgement.
Hence, the use of such theoretically calculated values of data communication delay may have an adverse effect upon the overall operation of such an information processing system.